Theoretical studies of elastohydrodynamic lubrication of artificial hip joints

Abstract

Theoretical studies of fluid-film lubrication in artificial hip joints are reviewed. The importance of developing effective numerical tools to solve realistic and complex lubrication problems in artificial hip joints has been emphasized. The elastic deformation of the bearing surfaces has been shown to play a dominant role in promoting elastohydrodynamic lubrication in various forms of artificial hip joints using different bearing surfaces. Both the bearing geometry and the structural supports can have a significant effect on the predicted lubricant film thickness. The importance of elastic deformation is further enhanced synergistically with the transient variation in load and speed to ensure a maximum effectiveness of the transient elastohydrodynamic lubrication mechanism in artificial hip joints. The recent application of the fast Fourier transform technique, in conjunction with the finite-element method to calculate the elastic deformation, not only enables more complex structural supports to the acetabular cup to be considered, but also offers the potential of analysing both transient and mixed lubrication problems in artificial hip joints.

Contact mechanics and lubrication analyses of ceramic-on-metal total hip replacements

“…Since the major velocity component 11 of hip implants is in the flexion/extension direction and the resultant load is in the 12 direction of about 10°medially to the vertical axis [19], it was possible to 13 approximate the conditions with an estimated small loss in accuracy by considering 14 only the flexion/extension velocity and vertical component of the load. In steady-state 15 EHL studies, the angular velocity around the z axis was adopted as 2 rad/s [17,20]. 16 The vertical load was chosen as 3000 N to represent approximately 4 times normal 17 body weight.…”

“…However, under 22 higher shear rates likely to be experienced in the hip joint (10 5 /s), it was considered 23 reasonable to assume the periprosthetic synovial fluid as Newtonian, isoviscous and 24 incompressible [20,[22][23][24]. A realistic viscosity of 0.002 Pa s was adopted for the 25 synovial fluid in the present study [23].…”

Contact mechanics and elastohydrodynamic lubrication in a novel metal-on-metal hip implant with an aspherical bearing surface

“…Since the major velocity component is in the flexion/extension direction, only the angular velocity around the z axis was considered with a value of 2 rad/s (Jin, 2006;Jagatia and Jin, 2001;. The vertical load was chosen as 3000 N to represent 4 times normal body weight.…”

“…The lubricant in artificial hip joints is periprosthetic synovial fluid, which behaves as a powerful non-Newtonian fluid under relatively low shear rates. However, under higher shear rates likely to be experienced in the hip joint (10 5 /s), it is reasonable to assume the periprosthetic synovial fluid as Newtonian, isoviscous and incompressible (Cook et al, 1978;Yao et al, 2003;Jin, 2006;Wang et al, 2008). A realistic viscosity of 0.002 Pa s was adopted (Yao et al, 2003).…”

“…Besides enhancing the wearresistance of bearing materials by choosing proper carbon content and using other treatments, improving the lubrication in hip implants is an alternative to reduce wear in terms of avoiding the direct contact between the bearing surfaces. Diameter and diametral clearance of hip bearings have been theoretically and experimentally found to be the key parameters of enhancing lubrication and minimizing wear (Medley et al, 2001;Smith et al, 2001;Dowson et al, 2004;Rieker et al, 2005;Jin, 2006;Liu et al, 2006b). Other factors such as structural supports and the wall thickness of the cup can also affect the contact pressure and lubrication performance in hip implants (Besong et al, 2001;Jagatia and Jin, 2002;Liu et al, 2003;Liu et al, 2004;Liu et al, 2006b).…”